import thenFs from 'then-fs'
thenFs.readFile('./txt/a.txt', 'utf8').then(res => {
    console.log(res);
    return thenFs.readFile('./txt/b.txt', 'utf8')
}).then(res => {
    console.log(res);
    return thenFs.readFile('./txt/c.txt', 'utf8')
}).then(res => {
    console.log(res);
})